Heat stress which results from work in areas of elevated temperature can be devastating especially where the work is done in confined spaces such as the crew spaces of an aircraft. In the aircraft situation, heat generating electronics within a modern aircraft generate an inordinate amount of heat in the closed area. This heat, especially when combined with solar radiation captured through the aircraft canopy, can cause the heat inside the closed area to rise to high levels. In the aircraft situation, the heat rise is aggravated when there are delays in the flight schedule. In flight, the cockpit area is cooled by the external environment and by an otherwise sufficient cooling system. One of the most susceptible parts of the pilot's anatomy to heat stress is his head, and this situation is made worse by capture and retention of heat radiated from the pilots head when the pilot is wearing a protective helmet. It is well known that a substantial part of the body's radiated heat is radiated from the scalp. In some aircraft, even on a moderate day, the temperature on the outside of a pilot's helmet may reach a temperature of 54.4.degree. C. (130.degree. F.) and the pilot's scalp temperature may reach a temperature of 43.3.degree. C. (110.degree. F.). Similar situations exist in other closed or heat producing areas in both military and industrial environments.
Introduction of air into a helmet for various purposes is well known in the prior art. In U.S. Pat. No. 4,095,289 to Kissen, et al., air is introduced into a pilot's helmet to provide air flow between the face of the user and the helmet visor. Cooled air for the pilot's head, provided through a plurality of discrete tubes with exit orifices in the tubes directed to discrete points on the pilots head, is shown in U.S. Pat. No. 4,100,320 to Chisum. An air cooled helmet of the plenum and controlled escape orifice is shown in U.S. Pat. No. 3,223,086.